The present invention relates to a method for the lateral positioning of a member relative to a joint, formed between two metal surfaces and having discontinuities or breaks, as well as to an apparatus for performing this method.
More specifically the present invention relates to the problem of the automatic lateral positioning of a member, such as a welding torch relative to a joint separating two parts to be welded, when said parts are held in position by previously made weld spots. These weld spots are generally produced manually in a random manner, so that their spacing and shape vary. Thus, these weld spots constitute discontinuities of the joint formed between the two parts, which are distributed in a random manner along the joint.
It is clear that the presence of these weld spots along the joint separating the two parts to be welded can disturb the operation of a welding head equipped with a device ensuring its automatic lateral positioning. Thus, the automatic positioning device may lose the joint at the time of passing the weld spot and consequently may guide the welding torch outside the working area.
These risks are particularly great when the automatic lateral positioning device uses eddy current sensors, because the latter very sensitively react to the weld spots, constituting a discontinuity of the joint separating metal surfaces, i.e. a short-circuit between the surfaces of the metal sheets to be welded. It is consequently not possible to control the welding torch directly as a function of the information supplied by the sensors, because this would lead to very significant position variations on passing the weld spots.
Obviously, the application to the welding of two metal sheets is not limitative and the invention can be used for solving any lateral positioning problem of a member relative to a joint formed between two metal surfaces and having discontinuities.
In the present state of the art there are on the one hand sensors which are in contact with the joint, and on the other hand sensors which are not in contact.
Among these sensors which are in contact with the joint, sensors of the passive type are known, which are constituted by sensing rods maintained in engagement with the joint and whose displacements are detected by position sensors making it possible to locate the joint in a plane transverse thereto. The behaviour of these detection systems on passing the weld spots is not satisfactory, because the rod can lose its guidance and can leave the joint. In certain cases, mechanical devices attachable to the end of the sensing rods make it possible to pass the weld spots, but such systems are not absolutely reliable.
Among sensors which are in contact with the joint, there are those of the active type also having a sensing rod connected to position sensors, as well as actuators making it possible to mobilize the rod. Such sensors make it possible to record the position of discontinuities along the joint during an operation in preparation for welding. During the actual welding operation, the device is then made inactive at the time when it passes the weld spots. However, in such a system, the recording operation is long and costly, so that it is inappropriate for solving the problem in question.
The known detection systems in contact with the metal sheets consequently fail to adequately solve the problem of passing weld spots in a joint formed between two metal surfaces. The prior art is even more limited with regards to contactless sensors, because no publication dealing with eddy current or other sensors (e.g. optical sensor) refers to the problem of passing weld spots.